// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Provides an implementation the parts of the RTree data structure that don't
// require knowledge of the generic key type. Don't use these objects directly,
// rather specialize the RTree<> object in r_tree.h. This file defines the
// internal objects of an RTree, namely Nodes (internal nodes of the tree) and
// Records, which hold (key, rectangle) pairs.

#ifndef UI_GFX_GEOMETRY_R_TREE_BASE_H_
#define UI_GFX_GEOMETRY_R_TREE_BASE_H_

#include <list>
#include <vector>

#include "base/containers/hash_tables.h"
#include "base/macros.h"
#include "base/memory/scoped_ptr.h"
#include "base/memory/scoped_vector.h"
#include "ui/gfx/geometry/rect.h"
#include "ui/gfx/gfx_export.h"

namespace gfx {

class GFX_EXPORT RTreeBase {
protected:
    class NodeBase;
    class RecordBase;

    typedef std::vector<const RecordBase*> Records;
    typedef ScopedVector<NodeBase> Nodes;

    RTreeBase(size_t min_children, size_t max_children);
    ~RTreeBase();

    // Protected data structure class for storing internal Nodes or leaves with
    // Records.
    class GFX_EXPORT NodeBase {
    public:
        virtual ~NodeBase();

        // Appends to |records_out| the set of Records in this subtree with rects
        // that intersect |query_rect|.  Avoids clearing |records_out| so that it
        // can be called recursively.
        virtual void AppendIntersectingRecords(const Rect& query_rect,
            Records* records_out) const = 0;

        // Returns all records stored in the subtree rooted at this node. Appends to
        // |matches_out| without clearing.
        virtual void AppendAllRecords(Records* records_out) const = 0;

        // Returns NULL if no children. Does not recompute bounds.
        virtual scoped_ptr<NodeBase> RemoveAndReturnLastChild() = 0;

        // Returns -1 for Records, or the height of this subtree for Nodes.  The
        // height of a leaf Node (a Node containing only Records) is 0, a leaf's
        // parent is 1, etc. Note that in an R*-Tree, all branches from the root
        // Node will be the same height.
        virtual int Level() const = 0;

        // Recomputes our bounds by taking the union of all child rects, then calls
        // recursively on our parent so that ultimately all nodes up to the root
        // recompute their bounds.
        void RecomputeBoundsUpToRoot();

        NodeBase* parent() { return parent_; }
        const NodeBase* parent() const { return parent_; }
        void set_parent(NodeBase* parent) { parent_ = parent; }
        const Rect& rect() const { return rect_; }
        void set_rect(const Rect& rect) { rect_ = rect; }

    protected:
        NodeBase(const Rect& rect, NodeBase* parent);

        // Bounds recomputation without calling parents to do the same.
        virtual void RecomputeLocalBounds();

    private:
        friend class RTreeTest;
        friend class RTreeNodeTest;

        // This Node's bounding rectangle.
        Rect rect_;

        // A weak pointer to our parent Node in the RTree. The root node will have a
        // NULL value for |parent_|.
        NodeBase* parent_;

        DISALLOW_COPY_AND_ASSIGN(NodeBase);
    };

    class GFX_EXPORT RecordBase : public NodeBase {
    public:
        explicit RecordBase(const Rect& rect);
        virtual ~RecordBase();

        virtual void AppendIntersectingRecords(const Rect& query_rect,
            Records* records_out) const OVERRIDE;
        virtual void AppendAllRecords(Records* records_out) const OVERRIDE;
        virtual scoped_ptr<NodeBase> RemoveAndReturnLastChild() OVERRIDE;
        virtual int Level() const OVERRIDE;

    private:
        friend class RTreeTest;
        friend class RTreeNodeTest;

        DISALLOW_COPY_AND_ASSIGN(RecordBase);
    };

    class GFX_EXPORT Node : public NodeBase {
    public:
        // Constructs an empty Node with |level_| of 0.
        Node();
        virtual ~Node();

        virtual void AppendIntersectingRecords(const Rect& query_rect,
            Records* records_out) const OVERRIDE;
        virtual scoped_ptr<NodeBase> RemoveAndReturnLastChild() OVERRIDE;
        virtual int Level() const OVERRIDE;
        virtual void AppendAllRecords(Records* matches_out) const OVERRIDE;

        // Constructs a new Node that is the parent of this Node and already has
        // this Node as its sole child. Valid to call only on root Nodes, meaning
        // Nodes with |parent_| NULL. Note that ownership of this Node is
        // transferred to the parent returned by this function.
        scoped_ptr<Node> ConstructParent();

        // Removes |number_to_remove| children from this Node, and appends them to
        // the supplied list. Does not repair bounds upon completion. Nodes are
        // selected in the manner suggested in the Beckmann et al. paper, which
        // suggests that the children should be sorted by the distance from the
        // center of their bounding rectangle to their parent's bounding rectangle,
        // and then the n closest children should be removed for re-insertion. This
        // removal occurs at most once on each level of the tree when overflowing
        // nodes that have exceeded the maximum number of children during an Insert.
        void RemoveNodesForReinsert(size_t number_to_remove, Nodes* nodes);

        // Given a pointer to a child node within this Node, removes it from our
        // list. If that child had any children, appends them to the supplied orphan
        // list. Returns the removed child. Does not recompute bounds, as the caller
        // might subsequently remove this node as well, meaning the recomputation
        // would be wasted work.
        scoped_ptr<NodeBase> RemoveChild(NodeBase* child_node, Nodes* orphans);

        // Returns the best parent for insertion of the provided |node| as a child.
        Node* ChooseSubtree(NodeBase* node);

        // Adds |node| as a child of this Node, and recomputes the bounds of this
        // node after the addition of the child. Returns the new count of children
        // stored in this Node. This node becomes the owner of |node|.
        size_t AddChild(scoped_ptr<NodeBase> node);

        // Returns a sibling to this Node with at least min_children and no greater
        // than max_children of this Node's children assigned to it, and having the
        // same parent. Bounds will be valid on both Nodes after this call.
        scoped_ptr<NodeBase> Split(size_t min_children, size_t max_children);

        size_t count() const { return children_.size(); }
        const NodeBase* child(size_t i) const { return children_[i]; }
        NodeBase* child(size_t i) { return children_[i]; }

    private:
        typedef std::vector<Rect> Rects;

        explicit Node(int level);

        // Given two arrays of bounds rectangles as computed by BuildLowBounds()
        // and BuildHighBounds(), returns the index of the element in those arrays
        // along which a split of the arrays would result in a minimum amount of
        // overlap (area of intersection) in the two groups.
        static size_t ChooseSplitIndex(size_t start_index,
            size_t end_index,
            const Rects& low_bounds,
            const Rects& high_bounds);

        // R*-Tree attempts to keep groups of rectangles that are roughly square
        // in shape. It does this by comparing the "margins" of different bounding
        // boxes, where margin is defined as the sum of the length of all four sides
        // of a rectangle. For two rectangles of equal area, the one with the
        // smallest margin will be the rectangle whose width and height differ the
        // least. When splitting we decide to split along an axis chosen from the
        // rectangles either sorted vertically or horizontally by finding the axis
        // that would result in the smallest sum of margins between the two bounding
        // boxes of the resulting split. Returns the smallest sum computed given the
        // sorted bounding boxes and a range to look within.
        static int SmallestMarginSum(size_t start_index,
            size_t end_index,
            const Rects& low_bounds,
            const Rects& high_bounds);

        // Sorts nodes primarily by increasing y coordinates, and secondarily by
        // increasing height.
        static bool CompareVertical(const NodeBase* a, const NodeBase* b);

        // Sorts nodes primarily by increasing x coordinates, and secondarily by
        // increasing width.
        static bool CompareHorizontal(const NodeBase* a, const NodeBase* b);

        // Sorts nodes by the distance of the center of their rectangles to the
        // center of their parent's rectangles.
        static bool CompareCenterDistanceFromParent(
            const NodeBase* a, const NodeBase* b);

        // Given two vectors of Nodes sorted by vertical or horizontal bounds,
        // populates two vectors of Rectangles in which the ith element is the union
        // of all bounding rectangles [0,i] in the associated sorted array of Nodes.
        static void BuildLowBounds(const std::vector<NodeBase*>& vertical_sort,
            const std::vector<NodeBase*>& horizontal_sort,
            Rects* vertical_bounds,
            Rects* horizontal_bounds);

        // Given two vectors of Nodes sorted by vertical or horizontal bounds,
        // populates two vectors of Rectangles in which the ith element is the
        // union of all bounding rectangles [i, count()) in the associated sorted
        // array of Nodes.
        static void BuildHighBounds(const std::vector<NodeBase*>& vertical_sort,
            const std::vector<NodeBase*>& horizontal_sort,
            Rects* vertical_bounds,
            Rects* horizontal_bounds);

        virtual void RecomputeLocalBounds() OVERRIDE;

        // Returns the increase in overlap value, as defined in Beckmann et al. as
        // the sum of the areas of the intersection of all child rectangles
        // (excepting the candidate child) with the argument rectangle. Here the
        // |candidate_node| is one of our |children_|, and |expanded_rect| is the
        // already-computed union of the candidate's rect and |rect|.
        int OverlapIncreaseToAdd(const Rect& rect,
            const NodeBase* candidate_node,
            const Rect& expanded_rect) const;

        // Returns a new node containing children [split_index, count()) within
        // |sorted_children|.  Children before |split_index| remain with |this|.
        scoped_ptr<NodeBase> DivideChildren(
            const Rects& low_bounds,
            const Rects& high_bounds,
            const std::vector<NodeBase*>& sorted_children,
            size_t split_index);

        // Returns a pointer to the child node that will result in the least overlap
        // increase with the addition of node_rect, or NULL if there's a tie found.
        // Requires a precomputed vector of expanded rectangles where the ith
        // rectangle in the vector is the union of |children_|[i] and node_rect.
        // Overlap is defined in Beckmann et al. as the sum of the areas of
        // intersection of all child rectangles with the |node_rect| argument
        // rectangle.  This heuristic attempts to choose the node for which adding
        // the new rectangle to their bounding box will result in the least overlap
        // with the other rectangles, thus trying to preserve the usefulness of the
        // bounding rectangle by keeping it from covering too much redundant area.
        Node* LeastOverlapIncrease(const Rect& node_rect,
            const Rects& expanded_rects);

        // Returns a pointer to the child node that will result in the least area
        // enlargement if the argument node rectangle were to be added to that
        // node's bounding box. Requires a precomputed vector of expanded rectangles
        // where the ith rectangle in the vector is the union of children_[i] and
        // |node_rect|.
        Node* LeastAreaEnlargement(const Rect& node_rect,
            const Rects& expanded_rects);

        const int level_;

        Nodes children_;

        friend class RTreeTest;
        friend class RTreeNodeTest;

        DISALLOW_COPY_AND_ASSIGN(Node);
    };

    // Inserts |node| into the tree. The |highest_reinsert_level| supports
    // re-insertion as described by Beckmann et al. As Node overflows progagate
    // up the tree the algorithm performs a reinsertion of the overflow Nodes
    // (instead of a split) at most once per level of the tree. A starting value
    // of -1 for |highest_reinsert_level| means that reinserts are permitted for
    // every level of the tree. This should always be set to -1 except by
    // recursive calls from within InsertNode().
    void InsertNode(scoped_ptr<NodeBase> node, int* highest_reinsert_level);

    // Removes |node| from the tree without deleting it.
    scoped_ptr<NodeBase> RemoveNode(NodeBase* node);

    // If |root_| has only one child, deletes the |root_| Node and replaces it
    // with its only descendant child. Otherwise does nothing.
    void PruneRootIfNecessary();

    // Deletes the entire current tree and replaces it with an empty Node.
    void ResetRoot();

    const Node* root() const { return root_.get(); }

private:
    friend class RTreeTest;
    friend class RTreeNodeTest;

    // A pointer to the root node in the RTree.
    scoped_ptr<Node> root_;

    // The parameters used to define the shape of the RTree.
    const size_t min_children_;
    const size_t max_children_;

    DISALLOW_COPY_AND_ASSIGN(RTreeBase);
};

} // namespace gfx

#endif // UI_GFX_GEOMETRY_R_TREE_BASE_H_
